Radiation (e.g. X-ray) detectors include an “indirect conversion type” detector which once generates light upon incidence of radiation (e.g. X rays) and generates electric charges from the light, thus detecting the radiation by converting the radiation indirectly into the electric charges, and a “direct conversion type” detector which generates electric charges upon incidence of radiation, thus detecting the radiation by converting the radiation directly into the electric charges. The electric charges are generated by a radiation sensitive semiconductor.
As shown in FIG. 10, a direct conversion type radiation detector has an active matrix substrate 51, a radiation sensitive semiconductor 52 for generating electric charges upon incidence of radiation, and a common electrode 53 for bias voltage application. The active matrix substrate 51 has a plurality of collecting electrodes (not shown) formed on a radiation incidence surface thereof, with an electric circuit (not shown) arranged for storing and reading electric charges collected by the respective collecting electrodes. The respective collecting electrodes are set in a two-dimensional matrix arrangement inside a radiation detection effective area SA.
The semiconductor 52 is laid on the incidence surfaces of the collecting electrodes formed on the active matrix substrate 51, and the common electrode 53 is formed and laid planarly on the incidence surface of the semiconductor 52. A lead wire 54 for bias voltage supply is connected to the incidence surface of the common electrode 53.
In time of radiation detection by the radiation detector, a bias voltage from a bias voltage source (not shown) is applied to the common electrode 53 for bias voltage application via the lead wire 54 for bias voltage supply. With the bias voltage applied, electric charges are generated by the radiation sensitive semiconductor 52 upon incidence of the radiation. The generated electric charges are first collected by the collecting electrodes. The electric charges collected by the collecting electrodes are fetched as radiation detection signals from the respective collecting electrodes by the storing and reading electric circuit including capacitors, switching elements, electric wires and so on.
Each of the collecting electrodes in the two-dimensional matrix arrangement corresponds to an electrode (pixel electrode) corresponding to each pixel in a radiographic image. By fetching radiation detection signals, it becomes possible to create a radiographic image according to a two-dimensional intensity distribution of the radiation projected to the radiation detection effective area SA.
However, the conventional radiation detector shown in FIG. 10 has a problem of performance degradation resulting from the lead wire 54 being connected to the common electrode 53. That is, since a hard metal wire such as copper wire is used for the lead wire 54 for bias voltage supply, damage occurs to the radiation sensitive semiconductor 52 when the lead wire 54 is connected to the common electrode 53, thereby causing performance degradation such as a voltage resisting defect.
Particularly where the semiconductor 52 is amorphous selenium or a non-selenic polycrystalline semiconductor such as CdTe, CdZnTe, PbI2, HgI2 or TlBr, the radiation sensitive semiconductor 52 of large area and thickness may easily be formed by vacuum deposition. However, such amorphous selenium and non-selenic polycrystalline semiconductor are relatively soft and vulnerable to damage.
In order to avoid the performance degradation resulting from the lead wire 54 being connecting to the common electrode 53, Inventors have proposed an invention as shown in FIG. 11 (see Patent Document 1, for example). As shown in FIG. 11 (corresponding to FIG. 2 of Patent Document 1), an insulating seat 55 is disposed on the incidence surface of the semiconductor 52 outside the radiation detection effective area SA. A common electrode 53 is formed to cover at least part of the seat 55, and a lead wire 54 is connected to a portion of the incidence surface of the common electrode 53 located on the seat 55.
With such seat 55 disposed, the seat 55 can reduce a shock occurring when the lead wire 54 is connected to the common electrode 53. This consequently prevents damage to the radiation sensitive semiconductor that leads to a voltage resisting defect, and avoids performance degradation such as voltage resisting defect. The seat 55 is disposed outside the radiation detection effective area SA, thereby preventing impairment of the radiation detecting function.
As shown in FIG. 12, there is a technique wherein a resin layer 57 of curable synthetic resin is formed to fix an auxiliary plate 56 so that the insulating auxiliary plate 56 having a thermal expansion coefficient nearly equal to that of an active matrix substrate 51 covers a semiconductor 52 and a common electrode 53. Further, the resin layer 57 is formed thicker outside a radiation detection effective area SA including a connection of the common electrode 53 to a lead wire 54 than inside the radiation detection effective area SA (see Patent Document 2, for example). With the resin layer 57 formed thinner inside the radiation detection effective area SA, stress on the semiconductor 52 due to the resin layer 57 can be reduced. With the resin layer 57 formed thicker outside the radiation detection effective area SA, performance degradation in creeping discharge prevention can be reduced.
[Patent Document 1]
Unexamined Patent Publication No. 2005-86059 (pages 1, 2, 4 to 12, FIGS. 1, 2, 6 to 9)
[Patent Document 2]
Unexamined Patent Publication No. 2005-286183 (pages 1 to 10, FIG. 1)